Graphene sheets are one-atom-thick planar sheets of sp2-bonded carbon. The strongest bond in nature, the C—C bond, covalently locks these atoms in place giving them remarkable mechanical properties. A suspended single layer of graphene is one of the stiffest known materials characterized by a remarkably high Young's modulus of ˜1 TPa. See, e.g., Bunch, J. S., et al., Nano Letters, Vol. 8, No. 8, pp. 2458-2462 (2008). Theoretical and experimental results on single layer graphene nanosheets exhibit extremely high values of elastic modulus (˜1,000 GPa), fracture strength (˜100-400 GPa), thermal conductivity (˜5,300 Wm−1 K−1), mobility of charge carriers (˜200,000 cm2 V−1 s−1), large surface area (up to >2,600 m2/g), and anomalous integer and fractional quantum Hall effect. These properties make graphene very promising for many applications such as solar cells and hydrogen storage, batteries, supercapacitors, sensors, and nanocomposites. See Stankovich, S., et al., Nature, Vol. 442, pp. 282-286 (2006) and Kuilla, T., et al., Prog. Polym. Sci., Vol. 35, pp. 1350-1375 (2010).
To exploit the exceptional strength and conductive properties of graphene sheets, numerous attempts have been made to incorporate graphene sheets into polymers. However, one of the problems encountered in making polymer-graphene composites is the difficulty in achieving good dispersion of the graphene in the blend. As degree of graphene dispersion improves, the strength properties of the polymer composite correspondingly improve as well.
Layers of graphene tend to tightly agglomerate due to Van der Waals forces. Dispersing graphene is difficult because graphene agglomerates can fall anywhere in the range of a few sheets to many hundreds of sheets thick. In order to obtain good graphene dispersion Van der Waals force must be overcome but conventional methods used to disperse the graphene, such as sonication, can also damage the crystal structure of the sheet and, consequently, impair strength and tensile properties. Similarly, prior art methods employed to improve dispersion of graphene in a polymer matrix, in particular chemical functionalization of graphene, preclude high levels of loading of the graphene sheets in the polymer composite thus compromising the strength of the composite material.
Accordingly, it is an object of the present invention to provide thin layers of graphene sheets intercalated with polymer platelets to produce a graphene/polymer composite having exceptional tensile strength and elongation-to-break characteristics when compared with the base polymer of the polymer composite.